There are dozens of theories about what happened to Ms Earhart. Did she starve to death on a remote atoll, or did she spy on the Japanese military build-up, only to be taken prisoner?

"Had she got this information back to the government, Pearl Harbour may never have happened," says Mr Marshall.

Ms Earhart's widower sold the Packard to a notorious gangster before a judge got hold of it. He tinkered with it for 50 years. Then Mr Marshall, an Australian, offered to swap it with a Buick, even before he learned its story.

"The car in itself is a treasure anyway, but to have such a history is just breath-taking," he says.